The present invention relates generally to a hologram and its holographic process, and more particularly to a security-conscious hologram that is much less vulnerable to illegal copying and can be easily told from any illegal copy forged from it, and a holographic process for the same.
Holograms, thanks to their aesthetic attributes, have been on the market also for prevention of illegal copying by visual authentication. Holograms appearing on the market, for the most part, have been of the embossed type fabricated with a variety of designs capable of visual authentication. However, such embossed holograms are now easier to fabricate, on the way out for prevention of illegal copying.
In this conjunction, the embossed type hologram has been a sort of expression wherein a certain direction parallax alone is intervened, and so a three-dimensional appearance is obtained in that direction alone. As a hologram comparable to the embossed type hologram, a volume hologram has been developed, foraying into the illegal copying preventive field. For the volume hologram capable of applying a three-dimensional appearance to the reconstructed image irrespective of vertical and horizontal directions, authentication is required by making a design difference with a conventional embossed hologram. When an ordinary model is holographically recorded in the volume hologram, it is possible to apply a three-dimensional appearance to the length direction as well as to the width direction. With some volume holograms, however, a reconstructed image cannot be easily in sight depending on object's solidity, light source, and design.
So far, a volume hologram for prevention of illegal copying with ordinarily invisible fine patterns three-dimensionally recorded in it has been known from Patent Publication 1 as an example. Even with this, however, it would be not easy to ensure such a sufficient three-dimensional appearance as mentioned above.
Patent Publication 1: JP-A 11-24538